The Horn of Africa has become a strategic linchpin for the United States, so the fact that China has dramatically escalated its involvement there presents a daunting challenge for U.S. policymakers. Nowhere is this more evident than in the tiny country of Djibouti, where Beijing is aggressively expanding its influence.

When China opened its first overseas military base in Djibouti last year, Washington took a wait-and-see approach. The United States, Japan, France and Italy all have bases in the area, so the Chinese military presence was a test case of whether Beijing’s military expansion in Africa would be an opportunity for cooperation or a source of potential conflict. A year later, the verdict is increasingly clear.

The Chinese military base is only one part of a steady encroachment into Djibouti that now threatens the diplomatic and national security interests of the United States and its allies.

Earlier this year, the Djiboutian government, which is heavily indebted to Beijing, seized control of Doraleh Container Terminal from Dubai-based DP World. Djibouti President Ismail Omar Guelleh invoked “emergency” measures to ignore legal rulings in the United Kingdom meant to prevent his seizure of the port.

The Djiboutian government is expected to hand over operations of the port to Chinese state-connected firms and in July announced a partnership with one of them to establish a massive free trade zone in the country. Situated along one of the busiest commercial sea lanes in the world, Chinese economic interests are clear. Djibouti stands to be a key node in China’s “string of pearls ” strategy, which links key ports to their greater “One Belt, One Road” initiative.

Meanwhile, Beijing’s military activities in Djibouti are of increasing concern. The U.S. base there is a key launching pad for anti-terrorism and intelligence operations against the Islamic State, al-Qaeda, al-Shabab and Boko Haram. The United States in May publicly accused China of using high-grade lasers to repeatedly attack U.S. pilots operating out of that base.

That prompted Congress to pass legislation last month that includes language requiring the Pentagon to provide a formal assessment of China’s military presence in Djibouti and the threat it poses to U.S. military personnel. Lawmakers are also concerned that Beijing is using its presence in Djibouti to facilitate an illicit arms-trade network that funnels money to the Guelleh regime.

“Guelleh’s dictatorial reign has been largely fueled by a steady flow of Chinese cash, palaces and gifts,” Rep. Mo Brooks (R-Ala.) wrote in a Sept. 24 letter to U.S. Ambassador to the United Nations Nikki Haley. “With new reports indicating his government is profiting from the burgeoning arms trade supplying Houthi rebels in Yemen and terrorist groups the U.S. is combatting across the African continent, it is time for his reckless and unscrupulous behavior to be firmly addressed by the United States.”

Over the past five years, China’s official arms sales to Africa have increased by 55 percent and its share of the African arms market has doubled to 17 percent, surpassing the United States, according to the Stockholm International Peace Research Institute. There is also growing evidence that Djibouti is emerging as a strategic transit node for illegal weapons smuggled between Yemen and places such as Somalia.

The Chinese government has a long history of fueling instability in Africa by trading in weapons with rogue regimes. China sent massive amounts of weapons to the Mugabe regime in Zimbabwe in 2008 while it was under a European Union arms embargo. Beijing long supplied arms to Sudanese dictator Omar al-Bashir that contributed to genocide in South Sudan.

What’s new is that, under President Xi Jinping, Beijing now has the power, influence and intention to combine its economic, diplomatic and military interference in Africa to wide-ranging effect.

“China’s strategy on the continent is a comprehensive one, including economic, political and security elements,” said Joshua Eisenman, assistant professor at the Lyndon B. Johnson School of Public Affairs at the University of Texas at Austin. “For years we’ve looked primarily at the economic side, but now, as China’s relations with Djibouti demonstrate, the political and security elements have become an increasingly important part of China’s relations with African states.”

The U.S. government, so far, seems unwilling or unable to confront the problem. A spokesman for the State Department’s Africa bureau told me that U.S. policy is not to curtail any other actor’s constructive involvement in Africa, but to encourage them insofar as their influence positively supports good governance, rule of law and anti-corruption efforts.

With regard to China’s involvement in Djibouti, that ship has sailed. The Trump administration needs to shift to an approach that places pressure on China to behave better in Djibouti and encourages the Guelleh government to reject Beijing’s scheme to turn that country into a Chinese vassal — before that instability further harms U.S. and African interests.

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Josh RoginJosh Rogin is a columnist for the Global Opinions section of The Washington Post. He writes about foreign policy and national security. Rogin is also a political analyst for CNN. He previously worked for Bloomberg View, the Daily Beast, Foreign Policy, Congressional Quarterly, Federal Computer Week and Japan's Asahi Shimbun newspaper. Follow